Communication device and communication method

ABSTRACT

A base station selects, from among a plurality of code sequences orthogonal to one another, one code sequence by which an uplink signal including a demodulation reference signal repeated in a plurality of subframes is multiplied and transmits, to a terminal for which transmission of the repeated uplink signal is configured, information indicating the selected code sequence by using a field for indicating a cyclic shift and an orthogonal sequence used for the demodulation reference signal. A terminal receives information indicating one of a plurality of code sequences orthogonal to one another using a field for indicating a cyclic shift and an orthogonal sequence used for a demodulation reference signal and multiplies an uplink signal including the demodulation reference signal repeated in a plurality of subframes by the code sequence indicated by the information.

BACKGROUND 1. Technical Field

The present disclosure relates to a communication device and acommunication method and, in particular, to a base station, a terminal,a transmission method, and a signal spreading method.

2. Description of the Related Art

In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution),OFDMA (Orthogonal Frequency Division Multiple Access) is adopted as acommunication method for a downlink from a base station (also referredto as an eNB) to a terminal (also referred to as a UE (User Equipment)).In addition, SC-FDMA (Single Carrier-Frequency Division Multiple Access)is adopted as a communication method for an uplink from a terminal to abase station (refer to, for example, 3GPP TS 36.211 V12.0.0, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical channels andmodulation,” December 2014; 3GPP TS 36.212 V12.0.0, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Multiplexing and channel coding,”December 2014; and 3GPP TS 36.213 V12.0.0, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical layer procedures,” December2014).

In LTE, a base station performs communication by allocating a resourceblock (RB) in the system band to the terminal for each unit of timecalled a subframe. FIG. 1 illustrates an example of a subframeconfiguration in an uplink shared channel (PUSCH: Physical Uplink SharedChannel). As illustrated in FIG. 1 , a subframe is formed from two timeslots. In each of the slots, a plurality of SC-FDMA data symbols and ademodulation reference signal (DMRS) are time-multiplexed. Uponreceiving the PUSCH, the base station performs channel estimation usingthe DMRS. Thereafter, the base station demodulates and decodes theSC-FDMA data symbol using the result of channel estimation.

In LTE-Advanced (also referred to as “LTE-A”), which is an expansion ofLTE, SU-MIMO (Single User-Multiple Input Multiple Output) is applied toPUSCH in order to improve the use efficiency of the uplink frequency. InSU-MIMO, a terminal can transmit a plurality of uplink data through onePUSCH by spatially multiplexing the data by using a plurality ofantennas. The base station receives and separates a plurality of signalssimultaneously transmitted from the terminal by using a plurality ofantennas.

In addition, MU-MIMO (Multi User-MIMO) is also employed in LTE-A.MU-MIMO is a technology that improves the spectral efficiency. InMU-MIMO, a plurality of terminals transmit data at the same time and atthe same frequency, and the base station separates signals transmittedfrom the plurality of terminals at the same time.

In LTE-A having SU-MIMO and MU-MIMO applied, in order to reduceinterference between DMRSs transmitted using the same time/frequencyresource, different cyclic shifts are applied to the DMRSs among theterminals, or two DMRSs in the PUSCH are multiplied by differentorthogonal codes (OCC: Orthogonal Cover Code) among the terminals sothat the plurality of DMRSs are orthogonally multiplexed.

In addition, in the downlink, the base station transmits downlinkcontrol information (L1/L2 control information) for informing theterminal of resource allocation for the uplink data. This downlinkcontrol information is transmitted from the base station to the terminalby using a downlink control channel, such as PDCCH (Physical DownlinkControl Channel), for example. The downlink control informationtransmitted from the base station in PDCCH is referred to as “DCI(Downlink Control Information)”.

When allocating resources for a plurality of terminals to one subframe,the base station transmits a plurality of DC's at the same time. At thistime, in order to identify the destination terminal of each of the DCIs,the base station adds, to the DCI, CRC (Cyclic Redundancy Check) bitsmasked (or scrambled) with the ID of the destination terminal andtransmits the DCI. Then, the terminal blind decodes the PDCCH byde-masking (or descrambling) the CRC bits of the DCI with the terminalID thereof so as to detect the DCI destined for the terminal itself.

The DCI for uplink includes DCI format 0 for indicating one-layertransmission without using SU-MIMO and DCI format 4 for indicating two-or more layer transmission using SU-MIMO. The DCI includes, for example,resource information about a resource allocated to the terminal by thebase station (resource allocation information) and MCS (Modulation andChannel Coding Scheme). The terminal controls, for example, the resourceand the MCS and transmits the PUSCH on the basis of the detected DCI.

In addition, the DCI for uplink includes information about cyclic shiftused for DMRS transmitted on PUSCH and information about OCC (refer to,for example, 3GPP TS 36.212 V12.0.0, “Evolved Universal TerrestrialRadio Access (E-UTRA); Multiplexing and channel coding,” December 2014).

Note that in recent years, as a mechanism for supporting the futureinformation society, M2M (Machine-to-Machine) communication whichrealizes a service through autonomous communication among deviceswithout user intervention has been expected. One of the specificapplications of the M2M system is a smart grid. A smart grid is aninfrastructure system that efficiently supplies a lifeline such aselectricity or gas. For example, in the smart grid, M2M communication isperformed between a smart meter installed in each of households orbuildings and a central server so that the smart grid controls thedemand balance of the resources autonomously and effectively. Otherexamples of the application of the M2M communication system include amonitoring system for goods management or remote medical care and remotemanagement of inventory and charging of a vending machine.

In the development of the M2M communication system, attention is focusedon the use of a cellular system that provides a particularly widecommunication area. 3GPP has been studying M2M based on a cellularnetwork in the standardization of LTE and LTE-Advanced with the name ofmachine type communication (MTC). In particular, 3GPP has been studying“Coverage Enhancement” that further expands the coverage area to supportMTC communication devices, such as a smart meter, installed in ablackspot of an existing communication area, such as a basement of abuilding (refer to, for example, RP-141660, Ericsson, Nokia Networks,“New WI proposal: Further LTE Physical Layer Enhancements for MTC”).

In particular, in order to further expand the communication area, MTCcoverage enhancement has been studying “Repetition” in which the samesignal is transmitted a plurality of times. More specifically, the studyof performing repetition transmission on the PUSCH has been conducted.At the base station which is the receiving side of the PUSCH, thereception signal power can be improved by combining the received signalstransmitted through reception transmission and, thus, the communicationarea can be expanded.

In repetition transmission, the same data signal is repeatedlytransmitted across a plurality of subframes (that is, time resources).Accordingly, in repetition transmission, the overhead increases, and thefrequency usage efficiency decreases. Therefore, when a terminal thatperforms MTC coverage enhancement (hereinafter also referred to as aterminal in an MTC coverage enhancement mode) performs repetitiontransmission on PUSCH, the following scheme has been studied (refer to,for example, R1-150311, Panasonic, “Multiple subframe code spreading forMTC UEs”). That is, spreading is performed across the subframes(hereinafter referred to as “multiple-subframe spreading”) bymultiplying the signals across a plurality of subframes of repetitiontransmission by an orthogonal code sequence (hereinafter referred to as“multiple-subframe spreading code” or a “multiple-subframe spreadingcode sequence). Thus, signals of a plurality of terminals can beorthogonally multiplexed across a plurality of subframes in whichrepetition transmission is performed and, thus, a decrease in thespectral efficiency of PUSCH can be reduced.

When multiple-subframe spreading is applied to the PUSCH, the basestation and the terminal need to share the multiple-subframe spreadingcode to be used in order for the base station to normally detect thesignal that is spread and code-multiplexed using the multiple-subframespreading code.

SUMMARY

One non-limiting and exemplary embodiment facilitates providing acommunication device and a communication method capable of sharing amultiple-subframe spreading code to be used between a base station and aterminal.

In one general aspect, the techniques disclosed here feature acommunication device including circuitry that selects, from among aplurality of code sequences orthogonal to one another, one code sequenceby which an uplink signal including a demodulation reference signalrepeated in a plurality of subframes is multiplied and a transmitterthat transmits, to a terminal for which transmission of the repeateduplink signal is configured, information indicating the selected codesequence by using a field for indicating a cyclic shift and anorthogonal code used for the demodulation reference signal.

According to the aspect of the present disclosure, a multiple-subframespreading code to be used can be shared between a base station and aterminal.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a PUSCH subframe configuration;

FIG. 2 illustrates an example of the multiple-subframe spreadingoperation;

FIG. 3 illustrates the configuration of the main portion of a basestation according to a first embodiment;

FIG. 4 illustrates the configuration of the main portion of a terminalaccording to the first embodiment;

FIG. 5 illustrates the configuration of the base station according tothe first embodiment;

FIG. 6 illustrates the configuration of the terminal according to thefirst embodiment;

FIG. 7A illustrates an existing DCI field used to indicate a cyclicshift and an OCC used for DMRS of LTE-A;

FIG. 7B illustrates an example of an MSCI for indicating amultiple-subframe spreading code according to the first embodiment;

FIG. 8 illustrates an example of an MSCI for indicating amultiple-subframe spreading code and a cyclic shift and an OCC used forDMRS according to a second embodiment;

FIG. 9 illustrates a combination of a multiple-subframe spreading code,a cyclic shift, and an OCC indicated by using the MSCI according to thesecond embodiment;

FIG. 10A illustrates an example of an MSCI for indicating amultiple-subframe spreading code and a cyclic shift and an OCC used forDMRS according to a variation of the second embodiment;

FIG. 10B illustrates a combination of a multiple-subframe spreadingcode, a cyclic shift, and an OCC indicated by using the MSCI accordingto the variation of the second embodiment;

FIG. 11A illustrates an example of an MSCI for indicating amultiple-subframe spreading code and a cyclic shift and an OCC used forDMRS according to a third embodiment;

FIG. 11B illustrates a combination of a multiple-subframe spreadingcode, a cyclic shift, and an OCC indicated by using the MSCI accordingto the third embodiment;

FIG. 12A illustrates an example of an MSCI for indicating amultiple-subframe spreading code and a cyclic shift and an OCC used forDMRS according to a fourth embodiment; and

FIG. 12B illustrates a combination of a multiple-subframe spreadingcode, a cyclic shift, and an OCC indicated by using the MSCI accordingto the fourth embodiment.

DETAILED DESCRIPTION Underlying Knowledge Forming Basis of the PresentDisclosure

In the case of sharing the multiple-subframe spreading code sequenceused between a base station and a terminal, the base station canallocate the multiple-subframe spreading code to the terminal on thebasis of the determination made by the base station in order to ensurethe flexibility of scheduling of the uplink.

However, to simply indicate the multiple-subframe spreading code to theterminal by using existing DCI for uplink, a field used to indicate themultiple-subframe spreading code to the terminal needs to be newly addedto the DCI format. For example, when the sequence length of themultiple-subframe spreading code is N_(SF), a field of ceil(log₂ N_(SF))bits is required and, thus, the overhead increases. Note that thefunction “ceil(X)” represents a ceiling function that returns thesmallest integer greater than or equal to X.

Therefore, according to an aspect of the present disclosure, acommunication device and a communication method are provided. Thecommunication device and the communication method are capable of sharinga multiple-subframe spreading code to be used between a base station anda terminal without increasing the overhead while ensuring theflexibility of uplink scheduling and increasing the overhead.

Embodiments of the present disclosure are described in detail below withreference to the accompanying drawings.

Overview of Communication System

The communication system according to each of the embodiments of thepresent disclosure is, for example, a system that supports LTE-Advanced.The communication system includes a base station 100 and a terminal 200as communication devices.

It is assumed that a plurality of terminals 200 in an MTC coverageenhancement mode exist in the cell of the base station 100. For example,when the MTC coverage enhancement mode is applied, the terminal 200transmits the PUSCH through repetition across a plurality of subframes(repetition transmission). In this case, for example, in the repetitiontransmission, the same signal is transmitted a plurality of times eachin one of the subframes. That is, the terminal 200 repeatedly transmitsthe same signal a number of times equal to a predetermined repetitionnumber in successive subframes equal in number to the predeterminedrepetition number (also referred to as a “repetition level” or“repetition factor”). At this time, the terminal 200 multiplies thesignals to be transmitted in the subframes through repetitiontransmission by the components of the multiple-subframe spreading codesequence, respectively (multiple-subframe spreading).

For example, when N_(Rep) repetitions are performed (that is, therepetition number: N_(Rep)), the terminal 200 repeatedly transmits thesignal of one subframe across the N_(Rep) subframes. At this time, theterminal 200 multiplies the signals transmitted through repetitiontransmission by the components of the multiple-subframe spreading codesequence, respectively. FIG. 2 illustrates an example of themultiple-subframe spreading for the PUSCH when the repetition numberN_(Rep) is 4 and the sequence length (or the spreading factor) N_(SF) ofthe multiple-subframe spreading code sequence is 4. The sequence lengthor the spreading factor N_(SF) of the multiple-subframe spreading codesequence may be the same as the repetition number N_(Rep) or may be apredetermined value (for example, a cell-specific value).

As described above, the terminal 200 set in the MTC coverage enhancementmode performs repetition on PUSCH in which data symbols and DMRSs aretime-multiplexed within one subframe across a plurality of subframes.Furthermore, the terminal 200 multiplies the signals each in one of aplurality of subframes by the components of one of a plurality ofmultiple-subframe spreading code sequences which are orthogonal to oneanother, respectively.

FIG. 3 is a block diagram illustrating the configuration of a mainportion of the base station 100 according to the embodiment of thepresent disclosure. In the base station 100 illustrated in FIG. 3 , acontrol unit 101 selects, from among a plurality of code sequencesorthogonal to one another, one code sequence to be multiplied by anuplink signal (PUSCH) that includes a demodulation reference signal andthat is subjected to repetition across a plurality of subframes. Thetransmitting unit 108 transmits, to a terminal (a terminal in the MTCcoverage enhancement mode) for which transmission of the uplink signalsubjected to repetition is configured, information indicating theselected one of the code sequences (downlink control information (DCI))by using a field for indicating a cyclic shift and an orthogonalsequence (OCC) used for the demodulation reference signal.

In addition, FIG. 4 is a block diagram illustrating the configuration ofa main portion of the terminal 200 according to each of the embodimentsof the present disclosure. In the terminal 200 illustrated in FIG. 4 ,when transmission of an uplink signal (PUSCH) subjected to repetition isconfigured (set) in the case of an MTC coverage enhancement mode), areceiving unit 202 receives information indicating one of a plurality ofcode sequences orthogonal to one another (downlink control information(DCI)) by using the field used for indicating a cyclic shift and anorthogonal sequence (OCC) used for the demodulation reference signal. Aspreading unit 212 multiplies the uplink signal including thedemodulation reference signal and subjected to repetition across aplurality of subframes by the code sequence indicated by the receivedinformation.

First Embodiment Configuration of Base Station

FIG. 5 is a block diagram illustrating the configuration of the basestation 100 according to a first embodiment of the present disclosure.In FIG. 5 , the base station 100 includes a control unit 101, a controlsignal generation unit 102, a coding unit 103, a modulation unit 104, asignal allocation unit 105, an IFFT (Inverse Fast Fourier Transform)unit 106, a CP (Cyclic Prefix) addition unit 107, a transmitting unit108, an antenna 109, a receiving unit 110, a CP removal unit 111, an FFT(Fast Fourier Transform) unit 112, a despreading unit 113, a demappingunit 114, a channel estimation unit 115, an equalization unit 116, ademodulation unit 117, a decoding unit 118, and a verification unit 119.

It should be noted that each of the configurations of the base station100 illustrated in FIG. 5 is only an example and, thus, can be replacedwith another configuration or removed. All of the configurations are notnecessarily required to practice the present disclosure.

The control unit 101 determines allocation of PUSCH to the terminal 200.For example, the control unit 101 determines (selects) a frequencyresource, a modulation/coding scheme, and a multiple-subframe spreadingcode to be allocated to the terminal 200. Thereafter, the control unit101 outputs information about the determined allocation of PUSCH to thecontrol signal generation unit 102.

In addition, the control unit 101 determines a coding level for thecontrol signal and outputs the determined coding level to the codingunit 103. In addition, the control unit 101 determines a radio resource(a downlink resource) to which the control signal is mapped and outputsinformation about the determined radio resource to the signal allocationunit 105.

The control signal generation unit 102 generates a control signaldestined for the terminal 200. The control signal includes an uplink DCIfor indicating the information about PUSCH allocation received from thecontrol unit 101. The uplink DCI is formed by a plurality of bits andincludes information indicating, for example, a frequency allocationresource and a modulation/coding scheme.

In addition, the uplink DCI for the terminal 200 in the MTC coverageenhancement mode (the terminal 200 that performs PUSCH repetitiontransmission across a plurality of subframes) includes an MSCI(Multiple-subframe spreading code indicator) for indicating themultiple-subframe spreading code to the terminal 200. The MSCI consistsof 3 bits or 2 bits. Furthermore, when the MSCI consists of 2 bits, theuplink DCI includes a 1-bit virtual CRC. Still furthermore, the uplinkDCI for terminals that are not in the MTC coverage enhancement mode(terminals that do not perform PUSCH repetition transmission across aplurality of subframes) includes information indicating the cyclic shiftand the OCC used for DMRS.

The control signal generation unit 102 generates a control informationbit string (a control signal) using the information input from thecontrol unit 101 and outputs the generated control signal to the codingunit 103. Note that the control signal generation unit 102 generates thebit string by including, in the control signal for each of the terminals200, the terminal ID of the terminal 200. For example, the CRC bitsmasked by the terminal ID are added to the control signal.

The coding unit 103 encodes the control signal (the coded bit string)received from the control signal generation unit 102 in accordance withthe coding level indicated by the control unit 101 and outputs the codedcontrol signal to the modulation unit 104.

The modulation unit 104 modulates the control signal received from thecoding unit 103 and outputs the modulated control signal (a symbolsequence) to the signal allocation unit 105.

The signal allocation unit 105 maps the control signal received from themodulation unit 104 to the radio resource indicated by the control unit101. Note that the control channel to which the control signal is mappedmay be a PDCCH for MTC or an EPDCCH (Enhanced PDCCH). The signalallocation unit 105 outputs, to the IFFT unit 106, a downlink subframesignal including the PDCCH for MTC or the EPDCCH to which the controlsignal is mapped.

The IFFT unit 106 performs IFFT processing on the signal received fromthe signal allocation unit 105 to convert the frequency domain signalinto a time domain signal. The IFFT unit 106 outputs the time domainsignal to the CP addition unit 107.

The CP addition unit 107 adds a CP to the signal received from the IFFTunit 106 and outputs, to the transmitting unit 108, the signal with theadded CP (an OFDM signal).

The transmitting unit 108 performs RF (Radio Frequency) processing, suchas D/A (Digital-to-Analog) conversion and up-conversion, on the OFDMsignal received from the CP addition unit 107 and transmits a radiosignal to the terminal 200 via the antenna 109.

The receiving unit 110 performs RF processing, such as down-conversionand A/D (Analog-to-Digital) conversion, on the uplink signal (PUSCH)received from the terminal 200 via the antenna 109 and outputs theobtained received signal to the CP removal unit 111. The uplink signal(PUSCH) transmitted from the terminal 200 includes the signals subjectedto repetition across a plurality of subframes and, thus, subjected tomultiple-subframe spreading.

The CP removal unit 111 removes the CP added to the reception signalreceived from the receiving unit 110 and outputs the signal after CPremoval to the FFT unit 112.

The FFT unit 112 performs FFT processing on the signal received from theCP removal unit 111 to decompose the signal into a signal sequence inthe frequency domain, extracts a signal corresponding to the subframe ofthe PUSCH, and outputs the extracted signal to the despreading unit 113.

The despreading unit 113 despreads the data signal and a signalcorresponding to the DMRS on the PUSCH subjected to repetitiontransmission and multiple-subframe spreading across a plurality ofsubframes by using the multiple-subframe spreading code to be used bythe terminal 200 for multiple-subframe spreading. For example, themultiple-subframe spreading code to be used by the terminal 200 formultiple-subframe spreading is indicated by the control unit 101. Thedespreading unit 113 outputs the despread signal to the demapping unit114.

The demapping unit 114 extracts, from the signal received from thedespreading unit 113, a subframe portion of the PUSCH allocated to theterminal 200. In addition, the demapping unit 114 decomposes theextracted subframe portion of the PUSCH of the terminal 200 into DMRSand a data symbol (a SC-FDMA data symbol). Thereafter, the demappingunit 114 outputs the DMRS to the channel estimation unit 115 and outputsthe data symbol to the equalization unit 116.

The channel estimation unit 115 performs channel estimation using theDMRS input from the demapping unit 114. The channel estimation unit 115outputs the obtained channel estimation value to the equalization unit116.

The equalization unit 116 equalizes the data symbol input from thedemapping unit 114 by using the channel estimation value input from thechannel estimation unit 115. The equalization unit 116 outputs theequalized data symbol to the demodulation unit 117.

The demodulation unit 117 applies IDFT (Inverse Discrete FourierTransform) processing to the SC-FDMA data symbol in the frequency domaininput from the equalization unit 116 to convert the SC-FDMA data symbolinto a time domain signal. Thereafter, the demodulation unit 117performs data demodulation on the signal. More specifically, thedemodulation unit 117 converts the symbol sequence into a bit string onthe basis of the modulation scheme specified for the terminal 200 to useand outputs the obtained bit string to the decoding unit 118.

The decoding unit 118 performs error correction decoding on the bitstring input from the demodulation unit 117 and outputs the decoded bitstring to the verification unit 119.

The verification unit 119 performs error detection on the bit stringinput from the decoding unit 118. Error detection is performed using theCRC bits added to the bit string. If the result of the CRC bitverification indicates no error, the verification unit 119 extracts thereceived data and outputs ACK. However, if the verification result ofthe CRC bits indicates the occurrence of an error, the verification unit119 outputs NACK. The ACK and NACK output from the verification unit 119are used in a retransmission control process performed by a control unit(not illustrated).

Configuration of Terminal

FIG. 6 is a block diagram illustrating the configuration of the terminal200 according to the first embodiment of the present disclosure. In FIG.6 , the terminal 200 includes an antenna 201, a receiving unit 202, a CPremoval unit 203, an FFT unit 204, an extraction unit 205, a controlunit 206, a DMRS generation unit 207, a coding unit 208, a modulationunit 209, a multiplexing unit 210, a DFT unit 211, a spreading unit 212,a signal allocation unit 213, an IFFT unit 214, a CP addition unit 215,and a transmitting unit 216.

It should be noted that each of the configurations of the terminal 200illustrated in FIG. 6 is only an example and, thus, can be replaced withanother configuration or removed. All of the configurations are notnecessarily required to practice the present disclosure.

The receiving unit 202 performs RF processing, such as down-conversionor AD conversion, on the radio signal (PDCCH or EPDCCH for MTC) from thebase station 100 received via the antenna 201 and obtains a basebandOFDM signal. The receiving unit 202 outputs the OFDM signal to the CPremoval unit 203.

The CP removal unit 203 removes the CP added to the OFDM signal receivedfrom the receiving unit 202 and outputs the signal after CP removal tothe FFT unit 204.

The FFT unit 204 performs FFT processing on the signal received from theCP removal unit 203 and, thus, converts the time domain signal into afrequency domain signal. The FFT unit 204 outputs the frequency domainsignal to the extraction unit 205.

The extraction unit 205 performs blind decoding on the frequency domainsignal received from the FFT unit 204 and determines whether the signalis a control signal destined for the terminal itself. The control signalhas CRC masked by the terminal ID and added thereto. Therefore, if theCRC verification is OK (no error) as a result of the blind decoding, theextraction unit 205 determines that the signal is control informationdestined for the terminal itself and outputs the control information tothe control unit 206. In addition, if the control signal includes avirtual CRC, the extraction unit 205 determines whether the controlsignal is a control signal destined for the terminal itself by using theresult of CRC verification and a bar channel CRC.

The control unit 206 controls PUSCH transmission on the basis of thecontrol signal input from the extraction unit 205. More specifically,the control unit 206 instructs the signal allocation unit to use theresource allocated to PUSCH transmission on the basis of the PUSCHresource allocation information included in the control signal. Inaddition, the control unit 206 instructs the coding unit 208 and themodulation unit 209 to use a coding method and a modulation scheme usedfor PUSCH transmission, respectively, on the basis of the informationabout the coding/modulation method included in the control signal.Furthermore, in the case of the MTC coverage enhancement mode (in thecase where repetition transmission is performed for PUSCH across aplurality of subframes), the control unit 206 determines themultiple-subframe spreading code used for PUSCH repetition transmissionon the basis of the MSCI included in the control signal and instructsthe spreading unit 212 to use the determined multiple-subframe spreadingcode. However, in the case of a mode other than the MTC coverageenhancement mode (in the case where repetition transmission is notperformed for PUSCH across a plurality of subframes), the control unit206 determines the cyclic shift and the OCC used for the DMRS on thebasis of the information that specifies the cyclic shift and the OCC tobe used for the DMRS and that is included in the uplink DCI and gives,to the DMRS generation unit 207, an instruction to use the determinedcyclic shift and OCC.

The DMRS generation unit 207 generates a DMRS in accordance with a DMRSpattern indicated by the control unit 206 and outputs the generated DMRSto the multiplexing unit 210.

The coding unit 208 adds the CRC bits masked by the terminal ID of theterminal 200 to the input transmission data (the uplink data) andperforms error correction coding. Thereafter, the coding unit 208supplies the encoded bit string to the modulation unit 209.

The modulation unit 209 modulates the bit string received from thecoding unit 208 and outputs the modulated signal (the data symbolsequence) to the multiplexing unit 210.

The multiplexing unit 210 time-multiplexes the data symbol sequenceinput from the modulation unit 209 and the DMRS input from the DMRSgeneration unit 207 within one subframe. Thereafter, the multiplexingunit 210 outputs the multiplexed signal to the DFT unit 211.

The DFT unit 211 applies DFT to the signal input from the multiplexingunit 210 and generates a frequency domain signal. Thereafter, the DFTunit 211 outputs the generated frequency domain signal to the spreadingunit 212.

If the terminal including the spreading unit 212 is in the MTC coverageenhancement mode, the spreading unit 212 performs repetition on a signalinput from the DFT unit 211 across a plurality of subframes andgenerates repetition signals. In addition, the spreading unit 212performs multiple-subframe spreading on the repetition signals by usingthe multiple-subframe spreading code specified by the control unit 206.Thereafter, the spreading unit 212 outputs the spread signal to thesignal allocation unit 213. That is, the spreading unit 212 multipliesthe repetition signals each in one of the subframes to be subjected torepetition by the components of the multiple-subframe spreading codesequence, respectively.

The signal allocation unit 213 maps the signal received from thespreading unit 212 to the time/frequency resources of the PUSCHspecified by the control unit 206. The signal allocation unit 213outputs, to the IFFT unit 214, the signal on the PUSCH to which thesignal is mapped.

The IFFT unit 214 generates a time domain signal by performing IFFTprocessing on the PUSCH signal in the frequency domain input from thesignal allocation unit 213. The IFFT unit 214 outputs the generatedsignal to the CP addition unit 215.

The CP addition unit 215 adds a CP to the time domain signal receivedfrom IFFT unit 214 and outputs, to the transmitting unit 216, the signalafter CP addition.

The transmitting unit 216 performs RF processing, such as D/A conversionand up-conversion, on the signal received from the CP addition unit 215and transmits a radio signal to the base station 100 via the antenna201.

Operation Performed by Base Station and Terminal

A method for sharing the multiple-subframe spreading code between thebase station 100 and terminal 200 having the above-describedconfigurations is described in detail below.

As described above, in the LTE-A, when SU-MIMO and MU-MIMO are applied,in order to reduce interference between the DMRSs transmitted using thesame time/frequency resource, the plurality of DMRSs are orthogonallymultiplexed in a subframe by applying different cyclic shifts to theDMRSs between the terminals or by multiplying two DMRSs in the PUSCH bydifferent OCCs among the terminals.

In addition, information about cyclic shift used for DMRS andinformation about OCC are indicated by using the uplink DCI. Morespecifically, among a plurality of DCI formats, DCI format 0 or DCIformat 4 uses 3 bits as a field for indicating the cyclic shift used forthe DMRS and the OCC.

Note that it is likely that MTC coverage enhancement is employed in anenvironment where the reception power of a desired signal from aterminal in a base station is very small. In addition, in such anenvironment, it is likely that an increase in communication capacity byusing MIMO is not needed and, thus, SU-MIMO and MU-MIMO are not used.

Furthermore, in MTC coverage enhancement, it is assumed thattransmission and reception using a narrow band of about 1.4 MHz in thesystem band is used in order to reduce the cost of terminals (refer to,for example, RP-141660, Ericsson, Nokia Networks, “New WI proposal:Further LTE Physical Layer Enhancements for MTC”). In LTE-A, it isstudied to increase the coverage enhancement effect by applyingfrequency hopping of the narrow band of 1.4 MHz within the system band(refer to, for example, RP-141660, Ericsson, Nokia Networks, “New WIproposal: Further LTE Physical Layer Enhancements for MTC”). Iffrequency hopping is applied, interference between neighboring cells canbe randomized by using different hopping patterns between theneighboring cells. Accordingly, it is likely that the operation for MTCcoverage enhancement is performed in an environment where there isalmost no interference between neighboring cells (an isolated cellenvironment).

As described above, in MTC coverage enhancement, it is likely that MIMOis not used and the operation is performed in an isolated cellenvironment. Therefore, in MTC coverage enhancement, it is highly likelythat a plurality of signals using the same time/frequency resource donot exist at the same time, and a plurality of terminals causing mutualinterference are not present at the same time. Note that when amultiple-subframe spreading code is used, a plurality of terminals usingthe same time/frequency resources at the same time are present, but itcan be said that the terminals are orthogonalized by code resourcessince different multiple-subframe spreading codes are used.

Accordingly, in MTC coverage enhancement, the need for orthogonalizationof DMRSs that is necessary in existing LTE-A is low. That is, in MTCcoverage enhancement, to reduce interference between DMRSs, the need tocontrol the cyclic shift and OCC used for DMRS among DMRSs is low. Forexample, any one pair of cyclic shift and OCC may be used. Thus, if, forexample, the cyclic shift and the OCC used by the terminal aredetermined in advance (are not dynamically changed), the cyclic shiftand the OCC need not be indicated from the base station to the terminal(need not be dynamically changed) by using the DCI.

Therefore, according to the present embodiment, to indicate themultiple-subframe spreading code to the terminal 200 in the MTC coverageenhancement mode, the base station 100 uses the existing DCI field,which is used to indicate the cyclic shift and the OCC used for theDMRS. That is, when repetition is applied to the PUSCH, the base station100 (the transmitting unit 108) uses the field for indicating the cyclicshift and the OCC used for DMRS transmitted on the PUSCH to transmitinformation (MSCI) indicating one multiple-subframe spreading codesequence selected from among a plurality of multiple-subframe spreadingcode sequences.

As an example, description is given with reference to the followingcase. That is, the terminal 200 is set in the MTC coverage enhancementmode, and multiple-subframe spreading using a multiple-subframespreading code having a sequence length (the code spreading factor)N_(SF)=8 is applied when PUSCH repetition transmission is performed.

The base station 100 indicates, to the terminal 200, the cyclic shiftand the OCC used by the terminal 200 for the DMRS in advance. The cyclicshift and the OCC used for DMRS may be predefined between the basestation 100 and the terminal 200. In addition, the base station 100 mayindicate, to the terminal 200, the cyclic shift and the OCC used for theDMRS via the higher layer.

The DMRS may be generated on the basis of the CAZAC (Constant AmplitudeZero Auto-Correlation) sequence, which is used in LTE Rel. 8 to 12 andhas excellent autocorrelation characteristics and mutual correlationcharacteristics, or a sequence other than the CAZAC sequence.

In addition, the base station 100 shares a plurality ofmultiple-subframe spreading codes that can be specified for the terminal200 with the terminal 200 in advance. The multiple-subframe spreadingcode that can be specified may be determined in advance between the basestation 100 and the terminal 200, or the base station 100 may indicate,to the terminal 200, the multiple-subframe spreading code via the higherlayer.

For example, when a Walsh sequence having a sequence length (codespreading factor) N_(SF)=8 is used as the multiple-subframe spreadingcode, the following eight multiple-subframe spreading codes can bespecified:

-   -   #0: (1, 1, 1, 1, 1, 1, 1, 1),    -   #1: (1, −1, 1, −1, 1, −1, 1, −1),    -   #2: (1, 1, −1, −1, 1, 1, −1, −1),    -   #3: (1, −1, −1, 1, 1, −1, −1, 1),    -   #4: (1, 1, 1, 1, −1, −1, −1, −1),    -   #5: (1, −1, 1, −1, −1, 1, −1, 1),    -   #6: (1, 1, −1, −1, −1, −1, 1, 1), and    -   #7: (1, −1, −1, 1, −1, 1, 1, −1).

The base station 100 transmits the uplink DCI to the terminal 200 viathe PDCCH for MTC or E P DCC H to specify the allocation resources ofthe PUSCH.

At this time, the uplink DCI includes information (MSCI) specifying amultiple-subframe spreading code. The MSCI is information that instructsthe terminal 200 to use a specific multiple-subframe spreading codeamong a plurality of candidates of the multiple-subframe spreading code.

That is, the base station 100 (the control unit 101 and the controlsignal generation unit 102) selects, from among the plurality ofcandidates of the multiple-subframe spreading code, a multiple-subframespreading code specified for the terminal 200 and generates an MSCIindicating the multiple-subframe spreading code. Thereafter, the basestation 100 transmits, to the terminal 200, the uplink DCI including thegenerated MSCI.

At this time, the base station 100 transmits the MSCI by using theexisting field for indicating the cyclic shift and the information aboutthe OCC used for the DMRS. That is, the base station 100 uses theexisting field for indicating the cyclic shift and the OCC used for DMRSto the terminal 200 set in the MTC coverage enhancement mode as a fieldfor indicating the multiple-subframe spreading code.

FIG. 7A illustrates an example of a field for indicating the cyclicshift and OCC used for DMRS. In FIG. 7A, the existing field forindicating the cyclic shift (n⁽²⁾ _(DMRS, λ)) and the information aboutOCC ([w^((λ))(0) w^((λ))(1)]) used for DMRS consists of 3 bits (000 to111).

In contrast, FIG. 7B illustrates an example of the field for indicatingthe multiple-subframe spreading code. As illustrated in FIG. 7B, for theMSCI for indicating the multiple-subframe spreading code, the existingfield having 3 bits (000 to 111) illustrated in FIG. 7A is used. Each ofthe values (000 to 111) represented by the 3 bits that constitute thefield is associated with one of the multiple-subframe spreading codesequences #0 to #7.

That is, FIG. 7B illustrates an example in which the existing 3-bitfield for indicating the cyclic shift and the OCC used for the DMRSillustrated in FIG. 7A is associated with an MSCI for indicating amultiple-subframe spreading code.

The terminal 200 (the extraction unit 205) performs blind decoding onthe received PDCCH for MTC or EPDCCH to obtain a DCI destined for theterminal 200 itself. Thereafter, if repetition across a plurality ofsubframes is applied to the PUSCH, the terminal 200 extracts the MSCIindicating the multiple-subframe spreading code sequence from the fieldof the received DCI for indicating the cyclic shift and the OCC used forthe DMRS transmitted on the PUSCH. By using the MSCI, the terminal 200(the control unit 206) selects one of the multiple-subframe spreadingcodes to be used by the terminal 200 from among a plurality of thecandidates of the multiple-subframe spreading code. Thereafter, theterminal 200 (the spreading unit 212) performs PUSCH repetitiontransmission in accordance with the determined multiple-subframespreading code.

Then, the base station 100 receives the PUSCH across the plurality ofsubframes transmitted from the terminal 200 and performsmultiple-subframe despreading using the multiple-subframe spreading codeused by the terminal 200. In addition, the base station 100 performschannel estimation on the basis of the DMRS extracted from the PUSCHsubframes after multiple-subframe despreading and performs equalization,repetition combining, demodulation, and decoding on the data symbol byusing the obtained channel estimation value.

As described above, according to the present embodiment, the basestation 100 transmits, to the terminal 200 set in the MTC coverageenhancement mode, the multiple-subframe spreading code (MSCI) by usingthe existing field (3 bits in FIG. 7A) for indicating the cyclic shiftand OCC used for DMRS.

In this manner, according to the present embodiment, themultiple-subframe spreading code can be shared between the base station100 and the terminal 200 without increasing the overhead.

Second Embodiment

When multiple-subframe spreading is used, the orthogonality needs to bemaintained among the multiple-subframe spreading code sequences for aperiod of time that is the spreading factor (the sequence length) of themultiple-subframe code spreading times the subframe period. For thisreason, as compared with code spreading within a subframe, intersymbolinterference tends to occur due to distortion of the orthogonality amongthe multiple-subframe spreading code sequences.

For DMRS, to improve the channel estimation accuracy, it is desirable tominimize the intersymbol interference.

Therefore, according to the present embodiment, a device and a methodcapable of suppressing the intersymbol interference among DMRSs by usingorthogonalization using the cyclic shift and OCC used for DMRS ofexisting LTE-A in addition to orthogonalization using amultiple-subframe spreading code are described.

Note that since a base station and a terminal according to the presentembodiment have basic configurations that are the same as those of thebase station 100 and the terminal 200 according to the first embodiment,the configurations are described with reference to FIGS. 5 and 6 .

As an example, the description below is given with reference to thefollowing case. That is, the terminal 200 is set in the MTC coverageenhancement mode, and multiple-subframe spreading using amultiple-subframe spreading code having a sequence length (the codespreading factor) N_(SF)=8 is applied when PUSCH repetition transmissionis performed.

The base station 100 shares a plurality of combinations of cyclic shiftand OCC used for DMRS, which can be provided to the terminal 200, withthe terminal 200 in advance. The combination of cyclic shift and OCCthat can be provided may be predefined between the base station 100 andthe terminal 200, or the base station 100 may provide the combinationsto the terminal 200 via the higher layer.

The DMRS is generated on the basis of the CAZAC (Constant Amplitude ZeroAuto-Correlation) sequence, which is used in LTE Rel. 8 to 12 and hasexcellent autocorrelation characteristics and mutual correlationcharacteristics.

In addition, the base station 100 shares a plurality ofmultiple-subframe spreading codes, which can be provided to the terminal200, with the terminal 200 in advance. The multiple-subframe spreadingcode that can be provided may be determined in advance between the basestation 100 and the terminal 200, or the base station 100 may providethe multiple-subframe spreading code to the terminal 200 via the higherlayer.

For example, when a Walsh sequence having a sequence length (a codespreading factor) N_(SF)=8 is used as the multiple-subframe spreadingcode, the following eight multiple-subframe spreading codes can bespecified:

-   -   #0: (1, 1, 1, 1, 1, 1, 1, 1),    -   #1: (1, −1, 1, −1, 1, −1, 1, −1),    -   #2: (1, 1, −1, −1, 1, 1, −1, −1),    -   #3: (1, −1, −1, 1, 1, −1, −1, 1),    -   #4: (1, 1, 1, 1, −1, −1, −1, −1),    -   #5: (1, −1, 1, −1, −1, 1, −1, 1),    -   #6: (1, 1, −1, −1, −1, −1, 1, 1), and    -   #7: (1, −1, −1, 1, −1, 1, 1, −1).

The base station 100 transmits the uplink DCI to the terminal 200 viathe PDCCH for MTC or EPDCCH to specify the allocation resources of thePUSCH.

At this time, like the first embodiment, the uplink DCI includesinformation (MSCI) indicating a multiple-subframe spreading code.

However, according to the present embodiment, in addition to themultiple-subframe spreading code, the MSCI specifies, for the terminal200, one of the combinations of cyclic shift and OCC selected from amonga plurality of combinations of cyclic shift and OCC used for DMRS.

That is, the base station 100 (the control unit 101 and the controlsignal generation unit 102) determines the multiple-subframe spreadingcode specified for the terminal 200 and the combination of the cyclicshift and the OCC used for the DMRS and generates an MSCI on the basisof the multiple-subframe spreading code and combination of cyclic shiftand OCC used for the DMRS. Thereafter, the base station 100 transmits,to the terminal 200, the uplink DCI including the generated MSCI.

That is, the base station 100 uses the existing field for indicating theinformation about the cyclic shift and information about the OCC usedfor DMRS to the terminal 200 set in the MTC coverage enhancement mode asa field for indicating the multiple-subframe spreading code and thecyclic shift and OCC used for DMRS.

FIG. 8 illustrates an example of a field for indicating themultiple-subframe spreading code and cyclic shift and OCC used for DMRS.As illustrated in FIG. 8 , the existing field consisting of 3 bits (000to 111) illustrated in FIG. 7A is used for MSCI that indicates themultiple-subframe spreading code and the cyclic shift and OCC used forDMRS. Each of the values (000 to 111) represented by the 3 bits thatconstitute the field is associated with one of the multiple-subframespreading code sequences #0 to #7 and one of the combinations of acyclic shift and an OCC.

That is, FIG. 8 illustrates an example in which the existing 3-bit fieldfor indicating the cyclic shift and the OCC used for the DMRSillustrated in FIG. 7A is associated with an MSCI for indicating amultiple-subframe spreading code and a cyclic shift and an OCC used forthe DMRS.

Note that in FIG. 8 , as an example, each of the values of MSCI isassociated with a combination of a cyclic shift and OCC at λ=0illustrated in FIG. 7A. However, the correspondence between an MSCI anda combination of a cyclic shift and an OCC is not limited to that inFIG. 8 . For example, the values of MSCI may be associated with thecombinations of a cyclic shift and an OCC at any one of λ=1 to 3illustrated in FIG. 7A. Alternatively, the values of MSCI may beassociated with combinations other than the above-describedcombinations.

The terminal 200 (the extraction unit 205) performs blind decoding onthe received PDCCH for MTC or EPDCCH to obtain a DCI destined for theterminal 200 itself. Thereafter, the terminal 200 in the MTC coverageenhancement mode extracts the MSCI, which indicates themultiple-subframe spreading code sequence, the cyclic shift, and theOCC, from the field of the received DCI for indicating the cyclic shiftand the OCC used for the DMRS. By using the MSCI, the terminal 200 (thecontrol unit 206) selects one of the multiple-subframe spreading codesused by the terminal 200 from among a plurality of the candidates of themultiple-subframe spreading code. In addition, by using the MSCI, theterminal 200 (the control unit 206) determines one combination of acyclic shift and an OCC used by the terminal 200 from the plurality ofcombinations of a cyclic shift and an OCC.

Thereafter, the terminal 200 (the DMRS generation unit 207) generates aDMRS in accordance with the determined combination of a cyclic shift andan OCC. In addition, the terminal 200 (the spreading unit 212) performsPUSCH repetition transmission in accordance with the determinedmultiple-subframe spreading code.

In contrast, the base station 100 receives the PUSCH across a pluralityof subframes transmitted from the terminal 200 and performsmultiple-subframe despreading using the multiple-subframe spreading codeused by the terminal 200. In addition, the base station 100 performschannel estimation on the basis of the DMRS extracted from the PUSCHsubframe after multiple-subframe despreading and performs equalization,repetition combining, demodulation, and decoding on the data symbol byusing the obtained channel estimation value.

As described above, like the first embodiment, according to the presentembodiment, the base station 100 indicates, to the terminal 200 set inthe MTC coverage enhancement mode, the multiple-subframe spreading codeby using the existing field (3 bits in FIG. 7A) for indicating thecyclic shift and OCC used for DMRS. In this manner, according to thepresent embodiment, like the first embodiment, the multiple-subframespreading code can be shared between the base station 100 and theterminal 200 without increasing the overhead.

In addition, according to the present embodiment, the base station 100indicates, to the terminal 200 set in the MTC coverage enhancement mode,the cyclic shift and the OCC used for DMRS in addition to themultiple-subframe spreading code by using the MSCI. In this manner,according to the present embodiment, the base station 100 can indicate,to the terminal 200, the cyclic shift and the OCC used for the DMRS byusing the DCI. As a result, even when multiple-subframe spreading isapplied, intersymbol interference caused by distortion of theorthogonality among the multiple-subframe spreading code sequences canbe prevented by orthogonalization of the DMRS and, thus, the occurrenceof intersymbol interference among the DMRSs can be prevented.

Variation of Second Embodiment

Sufficient suppression of intersymbol interference occurring betweenDMRSs by taking into account the orthogonality between multiple-subframespreading codes and the orthogonality between the DMRSs within asubframe by cyclic shift and OCC is discussed below.

FIG. 9 illustrates a multiple-subframe spreading code and a combinationof a cyclic shift and an OCC associated with each of the values (000 to111) of the MSCI illustrated in FIG. 8 on the cyclic shift axis and theorthogonal code axis. The value in a block illustrated in FIG. 9represents the value of the MSCI.

For example, intersymbol interference due to the movement of theterminal 200 easily occurs between the multiple-subframe spreading code#0 (1, 1, 1, 1, 1, 1, 1, 1) corresponding to MSCI=000 and themultiple-subframe spreading code #4 (1, 1, 1, 1, −1, −1, −1, −1)corresponding to MSCI=100 and, thus, the orthogonality is low. Generallyspeaking, the orthogonality between the code corresponding to the nthcolumn and the code corresponding to the (n+4)th column of theWalsh-Hadamard matrix (n=0 to 3) given by the following expression islow:

$\begin{matrix}\begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 \\1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} \\1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 \\1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 \\1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1}\end{bmatrix} & (1)\end{matrix}$

In addition, for example, between the DMRS that corresponds to MSCI=000and that uses the cyclic shift=0 and the OCC=[1 1] and the DMRS thatcorresponds to MSCI=100 and that uses the cyclic shift=2 and the OCC=[11], the cyclic shift difference is 2. Thus, the orthogonality betweenthe cyclic shift sequences is low, and the same OCC is used. Therefore,these DMRSs are susceptible to the influence of difference in thetransmission timing at the terminal 200 or a delay spread caused bymultipath.

As described above, mapping of the multiple-subframe spreading code,cyclic shift and OCC to an MSCI may have an impact on intersymbolinterference. Therefore, according to the present variation, a methodfor reducing intersymbol interference by associating a pair ofmultiple-subframe spreading codes having low mutual orthogonality withcyclic shifts (cyclic shift sequences) and OCCs having high mutualorthogonality is described.

More specifically, two cyclic shifts having a difference of the maximumvalue 6 are associated with two multiple-subframe spreading codescorresponding to the nth column and the (n+4)th column (n=0 to 3) of theWalsh-Hadamard matrix, respectively. The multiple-subframe spreadingcode, the cyclic shift, and the OCC which are associated in this mannerare associated with the MSCI.

FIG. 10A illustrates an example of a field for indicating themultiple-subframe spreading code and the cyclic shift and OCC used forDMRS. In FIG. 10A, the correspondence between the value represented by 3bits constituting the MSCI (000 to 111) and each of the cyclic shift andOCC is the same as in FIG. 8 .

For example, as illustrated in FIG. 10A, of the values (000 to 111)represented by 3 bits constituting the MSCI, the pair consisting of themultiple-subframe spreading code sequences #0 and #4 (the 0th and 4thcolumns of the Walsh-Hadamard matrix) having a low mutual orthogonalityamong the plurality of multiple-subframe spreading code sequences isassociated with MSCI=000 and MSCI=001 having a cyclic shift=0 and acyclic shift=6 associated therewith, respectively, whose difference is amaximum value of 6.

Similarly, as illustrated in FIG. 10A, the pair consisting of themultiple-subframe spreading code sequences #2 and #6 (the 2nd and 6thcolumns of the Walsh-Hadamard matrix) having a low mutual orthogonalityamong the plurality of multiple-subframe spreading code sequences isassociated with MSCI=010 and MSCI=111 having the cyclic shift=3 andcyclic shift=9 associated therewith, respectively, whose difference is amaximum value of 6. The same applies to each of the other values of theMSCI illustrated in FIG. 10A.

FIG. 10B illustrates a combination of a multiple-subframe spreading codeand a pair of a cyclic shift and an OCC (a combination associated witheach of the values (000 to 111) of the MSCI illustrated in FIG. 10A) onthe cyclic shift axis and the orthogonal code axis.

As illustrated in FIG. 10B, between the multiple-subframe spreading code#0 (1, 1, 1, 1, 1, 1, 1, 1) corresponding to MSCI=000 and themultiple-subframe spreading code #4 (1, 1, 1, 1, −1, −1, −1, −1)corresponding to MSCI=001, intersymbol interference caused by themovement of the terminal 200 easily occurs. However, as illustrated inFIG. 10B, the difference between the cyclic shifts respectivelyassociated with the multiple-subframe spreading code #0 and themultiple-subframe spreading code #4 is a maximum value of 6. That is,although intersymbol interference caused by the movement of the terminal200 easily occurs between the multiple-subframe spreading codesequences, the coding interference can be reduced by orthogonalizationbetween the DMRSs associated with these subframe spreading codesequences.

By associating a pair of multiple-subframe spreading codes having lowmutual orthogonality with a cyclic shift and an OCC having high mutualorthogonality in this manner, the intersymbol interference can bereduced.

Note that according to the present embodiment, the combination of acyclic shift and an OCC used for DMRS is the same as the combination ofa cyclic shift and an OCC in the existing LTE-A at λ=0 illustrated inFIG. 7A. In this way, the need for indicating the combination for MTCcoverage enhancement is eliminated since a plurality of combinations ofa cyclic shift and an OCC have already been indicated beforetransmission/reception of PUSCH.

Third Embodiment

According to the present embodiment, description is given with referenceto the case in which the number of candidates of the multiple-subframespreading code (the number of usable multiple-subframe spreading codes)to be indicated to a terminal set in the MTC coverage enhancement modeis smaller than the number of values indicated by using a number of bitsconstituting the existing field for indicating the cyclic shift and theOCC used for DMRS (the number of values represented by the bits).

Since the base station and the terminal according to the presentembodiment have basic configurations that are the same as those of thebase station 100 and the terminal 200 according to the first embodiment.Accordingly, description is given with reference to FIGS. 5 and 6 .

According to the present embodiment, as an example, the following caseis described. That is, the terminal 200 is set in the MTC coverageenhancement mode, and multiple-subframe spreading using amultiple-subframe spreading code having a sequence length (the codespreading factor) N_(SF)=4 is applied when PUSCH repetition transmissionis performed. In addition, the existing field used to indicate a cyclicshift and the OCC used for DMRS consists of 3 bits.

Furthermore, according to the present embodiment, like the secondembodiment, a combination of cyclic shift and OCC used for DMRS at λ=0of the existing LTE-A illustrated in FIG. 7A is associated with an MSCI.By making the combination of cyclic shift and OCC used for DMRS the sameas the combination in existing LTE-A, the need for indicating thecombination for MTC coverage enhancement is eliminated since a pluralityof combinations of a cyclic shift and an OCC have already been indicatedbefore transmission/reception of PUSCH.

Like the second embodiment, the base station 100 shares a plurality ofcombinations of cyclic shift and OCC used for DMRS with the terminal200, which can be specified for the terminal 200 in advance. Inaddition, like the second embodiment, the base station 100 shares aplurality of multiple-subframe spreading codes that can be specified forthe terminal 200 with the terminal 200 in advance.

For example, when a Walsh sequence having a sequence length (a spreadingfactor) N_(SF)=4 is used as the multiple-subframe spreading code, thefollowing four multiple-subframe spreading codes can be specified:

-   -   #0: (1, 1, 1, 1)    -   #1: (1, −1, 1, −1),    -   #2: (1, 1, −1, −1), and    -   #3: (1, −1, −1, 1).

In addition, the multiple-subframe spreading code that can be specifiedis expressed by using Walsh-Hadamard as follows:

$\begin{matrix}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix} & (2)\end{matrix}$

FIG. 11A illustrates an example of a field for indicating themultiple-subframe spreading code and cyclic shift and OCC used for DMRS.As illustrated in FIG. 11A, when the spreading factor N_(SF) of themultiple-subframe spreading code=4, the correspondence between an MSCI(3 bits) and a multiple-subframe spreading code (the number ofcandidates: 4) is not a one-to-one correspondence. That is, onemultiple-subframe spreading code is associated with two MSCIs.

Here, it is assumed that signals from a plurality of terminals 200 arenot multiplexed by using the same time/frequency resources and the samemultiple-subframe spreading code at the same time. That is, among theplurality of terminals 200, it is assumed that the above-described twoMSC's associated with one multiple-subframe spreading code are not usedat the same time.

Therefore, according to the present embodiment, one multiple-subframespreading code is associated with two cyclic shifts having low mutualorthogonality. In this manner, intersymbol interference can be reduced.

For example, as illustrated in FIG. 11A, the multiple-subframe spreadingcode #0 is associated with cyclic shift=0 and cyclic shift=2 having acyclic shift difference of 2. The multiple-subframe spreading code #1 isassociated with cyclic shift=3 and cyclic shift=4 having a cyclic shiftdifference of 1. The multiple-subframe spreading code #2 is associatedwith cyclic shift=6 and cyclic shift=8 having a cyclic shift differenceof 2. The multiple-subframe spreading code #3 is associated with cyclicshift=9 and cyclic shift=10 having a cyclic shift difference of 1.

In addition, like the second embodiment, a pair of multiple-subframespreading codes having low mutual orthogonality is associated with aDMRS using cyclic shift and OCC with high mutual orthogonality. In thismanner, intersymbol interference can be reduced. More specifically, asillustrated in FIG. 11A, two multiple-subframe spreading codescorresponding to the nth column and the (n+2)th column (n=0 to 1) of theWalsh-Hadamard matrix are associated with two cyclic shifts having amaximum difference of 6, respectively. The multiple-subframe spreadingcode, the cyclic shift, and the OCC which are associated in this mannerare associated with an MSCI.

For example, as illustrated in FIG. 11A, of the values (000 to 111)represented by 3 bits constituting the MSCI, MSCI=000 and MSCI=001having a cyclic shift=0 and a cyclic shift=6 associated therewith,respectively, whose difference is a maximum value of 6 are associatedwith a pair consisting of the multiple-subframe spreading code sequences#0 and #2 (the 0th and 2nd columns of the Walsh-Hadamard matrix) havinglow mutual orthogonality among the plurality of multiple-subframespreading code sequences. Similarly, MSCI=100 and MSCI=101 having acyclic shift=2 and a cyclic shift=8 associated therewith, respectively,whose difference is a maximum value of 6 are associated with the pairconsisting of the multiple-subframe spreading code sequences #0 and #2.

Still similarly, as illustrated in FIG. 11A, MSCI=010 and MSCI=111having a cyclic shift=3 and a cyclic shift=9 associated therewith,respectively, whose difference is a maximum value of 6 are associatedwith a pair consisting of the multiple-subframe spreading code sequences#1 and #3 (the 1st and 3rd columns of the Walsh-Hadamard matrix) havinglow mutual orthogonality among the plurality of multiple-subframespreading code sequences. Still similarly, MSCI=011 and MSCI=110 havinga cyclic shift=4 and a cyclic shift=10 associated therewith,respectively, whose difference is a maximum value of 6 are alsoassociated with the pair consisting of the multiple-subframe spreadingcode sequences #1 and #3.

FIG. 11B illustrates a multiple-subframe spreading code and acombination of the cyclic shift and OCC which are associated with eachof the values (000 to 111) of the MSCI illustrated in FIG. 11A, on thecyclic shift axis and the orthogonal code axis.

As illustrated in FIG. 11B, the same multiple-subframe spreading codesequence is associated with two neighboring cyclic shifts among thecyclic shifts associated with the MSCI (usable cyclic shifts).

For example, the two cyclic shifts respectively associated with themultiple-subframe spreading code #0 corresponding to MSCI=000 and themultiple-subframe spreading code #0 corresponding to MSCI=100 have adifference of 2, and the same OCC is combined with the two shift codes.Accordingly, the orthogonality is low. However, the samemultiple-subframe spreading code is associated with these resources, andthe resources are not used by a plurality of terminals 200 at the sametime. This also applies to the other multiple-subframe spreading codesequences #1 to #3 illustrated in FIG. 11B.

In FIG. 11B, if the cyclic shift difference between neighboring cyclicshifts associated with the same multiple-subframe spreading codesequence is 2 (in the case of the multiple-subframe spreading codesequence #0 or #2), the OCCs which are combined with the cyclic shiftsare the same. In contrast, if the cyclic shift difference betweenneighboring cyclic shifts having the same multiple-subframe spreadingcode sequence associated therewith is 1 (in the case of themultiple-subframe spreading code sequence #1 or #3), the OCCs which arecombined with the cyclic shifts differ from each other.

As described above, by associating the same multiple-subframe spreadingcode with the DMRSs that use cyclic shift and OCC with low mutualorthogonality, setting of these DMRSs by a plurality of the terminals200 at the same time can be prevented and, thus, intersymbolinterference can be reduced.

Furthermore, as illustrated in FIG. 11B, between the multiple-subframespreading code #0 (1, 1, 1, 1) corresponding to MSCI=000 and themultiple-subframe spreading code #2 (1, 1, −1, −1) corresponding toMSCI=001, intersymbol interference caused by the movement of theterminal 200 easily occurs. However, as illustrated in FIG. 11B, thedifference between the cyclic shifts respectively associated with themultiple-subframe spreading code #0 and the multiple-subframe spreadingcode #2 is 6, which is a maximum value. By associating a pair ofmultiple-subframe spreading codes having low mutual orthogonality with acyclic shift and OCC having high mutual orthogonality in this manner,the intersymbol interference can be reduced, as in the secondembodiment.

As described above, according to the present embodiment, if the numberof candidates of multiple-subframe spreading codes (the number of usablemultiple-subframe spreading codes) is smaller than the number of valuesthat can be represented by a number of bits constituting the existingfield for indicating the cyclic shift and the OCC used for DMRS, thecyclic shifts having low mutual orthogonality are associated with onemultiple-subframe spreading code. In this manner, intersymbolinterference caused by a decrease in the orthogonality between DMRSs canbe prevented.

In addition, according to the present embodiment, cyclic shifts havinghigh mutual orthogonality are associated with multiple-subframespreading codes having low mutual orthogonality. In this manner, codinginterference between the DMRSs due to distortion of the orthogonalitybetween the multiple-subframe spreading code sequences caused by theorthogonalization of the DMRS can be prevented.

Furthermore, according to the present embodiment, like the firstembodiment, a multiple-subframe spreading code can be shared between thebase station 100 and the terminal 200 without increasing the overhead.

Fourth Embodiment

According to the present embodiment, like the third embodiment,description is given with reference to the case in which the number ofcandidates of the multiple-subframe spreading code (the number of usablemultiple-subframe spreading codes) to be indicated to a terminal set inthe MTC coverage enhancement mode is smaller than the number of valuesthat can be represented by a number of bits constituting the existingfield for indicating the cyclic shift and the OCC used for DMRS.

In the third embodiment, description has been given with reference tothe case in which the multiple-subframe spreading code is associatedwith a plurality of MSCI. In contrast, according to the presentembodiment, description is given with reference to the case in which themultiple-subframe spreading codes are associated one to one with MSCIs.

Since the base station and the terminal according to the presentembodiment have basic configurations that are the same as those of thebase station 100 and the terminal 200 according to the first embodiment,description is given with reference to FIGS. 5 and 6 .

According to the present embodiment, as an example, the following caseis described. That is, a terminal 200 is set in the MTC coverageenhancement mode, and multiple-subframe spreading using amultiple-subframe spreading code having a sequence length (a codespreading factor) N_(SF)=4 is applied when PUSCH repetition transmissionis performed. In addition, the existing field used to indicate thecyclic shift and OCC used for DMRS consists of 3 bits.

Like the second embodiment, the base station 100 shares a plurality ofcombinations of cyclic shift and OCC used for DMRS with the terminal200, which can be specified for the terminal 200, in advance. Inaddition, like the second embodiment, the base station 100 shares aplurality of multiple-subframe spreading codes that can be specified forthe terminal 200 with the terminal 200 in advance.

In addition, when a Walsh sequence having a sequence length (a spreadingfactor) N_(SF)=4 is used as the multiple-subframe spreading code, thefollowing four multiple-subframe spreading codes can be specified:

-   -   #0: (1, 1, 1, 1),    -   #1: (1, −1, 1, −1),    -   #2: (1, 1, −1, −1), and    -   #3: (1, −1, −1, 1).

When the spreading factor N_(SF) of the multiple-subframe spreadingcode=4, the number of the multiple-subframe spreading code sequences is4. Therefore, the number of bits required for indicating themultiple-subframe spreading code having a spreading factor N_(SF)=4 is2. That is, like the first embodiment, when the existing field (3 bits)for indicating cyclic shift and OCC used for DMRS is used for indicatinga multiple-subframe spreading code, only 2 bits out of the 3 bits areneeded and, thus, the remaining 1 bit is an unused bit.

Therefore, according to the present embodiment, the base station 100uses 2 bits of the existing field (3 bits) for indicating cyclic shiftand OCC used for DMRS to indicate the MSCI and indicates themultiple-subframe spreading code and cyclic shift and OCC used for DMRSby using the MSCI.

FIG. 12A illustrates an example of a field for indicating themultiple-subframe spreading code and cyclic shift and OCC used for DMRS.In FIGS. 12A and 12B, a multiple-subframe spreading code sequence and acombination of a cyclic shift and an OCC are associated with each of thevalues (00 to 11) represented by 2 bits, which are required forindicating a multiple-subframe spreading code sequence, of the existingfield (3 bits) for Indicating the cyclic shift and OCC used for DMRS.

In addition, like the second embodiment, a pair of multiple-subframespreading codes having low mutual orthogonality is associated with aDMRS using cyclic shift and OCC having high mutual orthogonality. Inthis manner, intersymbol interference can be reduced. More specifically,as illustrated in FIG. 12A, two multiple-subframe spreading codescorresponding to the nth column and the (n+2)th column (n=0 to 1) of theWalsh-Hadamard matrix are associated with two cyclic shifts having amaximum difference of 6, respectively. The multiple-subframe spreadingcode, the cyclic shift, and the OCC which are associated in this mannerare associated with an MSCI.

For example, as illustrated in FIG. 12A, of the values (00 to 11)represented by 2 bits constituting the MSCI, MSCI=00 and MSCI=01 havingthe cyclic shift=0 and cyclic shift=6 associated therewith,respectively, whose difference is a maximum value of 6 are associatedwith the pair consisting of the multiple-subframe spreading codesequences #0 and #2 (the 0th and 2nd columns of the Walsh-Hadamardmatrix) having low mutual orthogonality among the plurality ofmultiple-subframe spreading code sequences.

Similarly, as illustrated in FIG. 12A, MSCI=10 and MSCI=11 having thecyclic shift=3 and cyclic shift=9 associated therewith, respectively,whose difference is a maximum value of 6 are associated with the pairconsisting of the multiple-subframe spreading code sequences #1 and #3(the 1st and 3rd columns of the Walsh-Hadamard matrix) having low mutualorthogonality among the plurality of multiple-subframe spreading codesequences.

FIG. 12B illustrates a multiple-subframe spreading code and acombination of the cyclic shift and OCC associated with each of thevalues (00 to 11) of the MSCI illustrated in FIG. 12A on the cyclicshift axis and the orthogonal code axis.

As illustrated in FIG. 12B, between the multiple-subframe spreading code#0 (1, 1, 1, 1) corresponding to MSCI=00 and the multiple-subframespreading code #2 (1, 1, −1, −1) corresponding to MSCI=01, intersymbolinterference caused by the movement of the terminal 200 easily occurs.However, as illustrated in FIG. 12B, the difference between the cyclicshifts respectively associated with the multiple-subframe spreading code#0 and the multiple-subframe spreading code #2 is 6, which is a maximumvalue.

In this manner, by associating the pair of multiple-subframe spreadingcodes having low mutual orthogonality with the cyclic shift and OCChaving high mutual orthogonality, intersymbol interference can bereduced.

In addition, according to the present embodiment, in the existing fields(3 bits) used for indicating the cyclic shift and the OCC used for DMRS,2 bits are used for an MSCI. The remaining 1 bit is used as a known bitby both the base station 100 and the terminal 200 (that is, a virtualCRC). That is, the existing field (3 bits) for indicating the cyclicshift and OCC used for DMRS is formed from the MSCI and virtual CRC.

The terminal 200 (extraction unit 205) de-masks (or descrambles) the CRCbits added to the DCI that may be destined for the terminal 200 itselfby using the terminal ID thereof and blind-decodes the PDCCH by usingthe CRC bit string and the virtual CRC bit. Thus, the terminal 200detects the DCI destined therefor.

In this manner, the terminal 200 can use the virtual CRC in addition tothe check result of the CRC bits in determining whether the received DCIis destined therefor. For example, even when the result of checking theCRC bits subjected to descrambling using the terminal ID of the terminal200 is successful, the terminal 200 can ignore the DCI if the virtualCRC bit included in the received DCI is not the same as the known bit.

Thus, detection error of control information by the terminal 200 can bereduced. Reduction of detection error contributes to expansion of thecoverage.

Each of the embodiments of the present disclosure has been describedabove.

Note that the values of the number of repetition, the cyclic shifts usedfor DMRS, the sequence lengths of OCC, and the sequence lengths ofmultiple-subframe spreading code sequence used in the above embodimentsare only examples and are not limited to the above-described values.

Furthermore, the present disclosure can be realized by software,hardware, or software in cooperation with hardware.

It should be noted that each functional block used in the description ofeach embodiment described above can be partly or entirely realized by anLSI such as an integrated circuit, and each process described in theeach embodiment may be controlled partly or entirely by the same LSI ora combination of LSIs. The LSI may be individually formed as chips, orone chip may be formed so as to include a part or all of the functionalblocks. The LSI may include a data input and output coupled thereto. TheLSI here may be referred to as an IC, a system LSI, a super LSI, or anultra LSI depending on a difference in the degree of integration.

In addition, the technique of implementing an integrated circuit is notlimited to the LSI and may be realized by using a dedicated circuit, ageneral-purpose processor, or a special-purpose processor. In addition,a FPGA (Field Programmable Gate Array) that can be programmed after themanufacture of the LSI or a reconfigurable processor in which theconnections and the settings of circuit cells disposed inside the LSIcan be reconfigured may be used. The present disclosure can be realizedas digital processing or analogue processing.

Furthermore, if future integrated circuit technology replaces LSIs as aresult of the advancement of semiconductor technology or otherderivative technology, the functional blocks could be integrated usingthe future integrated circuit technology. Biotechnology can also beapplied.

According to the present disclosure, a communication device includes acontrol unit that selects, from among a plurality of code sequencesorthogonal to one another, one code sequence by which an uplink signalincluding a demodulation reference signal subjected to repetition acrossa plurality of subframes is multiplied and a transmitting unit thattransmits, to a terminal for which transmission of the uplink signalsubjected to the repetition is configured, information indicating theselected code sequence by using a field for indicating a cyclic shiftand an orthogonal code used for the demodulation reference signal.

In addition, in the communication device according to the presentdisclosure, the plurality of code sequences are associated one to onewith a plurality of values indicated by using bits constituting thefield.

In addition, in the communication device according to the presentdisclosure, the plurality of values indicated by using bits constitutingthe field are associated one to one with a plurality of combinations ofthe code sequence, the cyclic shift, and the orthogonal sequence.

In addition, in the communication device according to the presentdisclosure, among a plurality of values indicated by using the bitsconstituting the field, two values which are associated one to one withtwo cyclic shifts having a maximum cyclic shift difference areassociated with two code sequences having low mutual orthogonality amongthe plurality of code sequences.

In addition, in the communication device according to the presentdisclosure, if the number of the plurality of code sequences is smallerthan the number of values indicated by using bits constituting thefield, one code sequence is associated with two of the values that areassociated with neighboring cyclic shifts.

In addition, in the communication device according to the presentdisclosure, if the number of the plurality of code sequences is smallerthan the number of values indicated by using bits constituting thefield, a plurality of values indicated by using, among the bits, anumber of bits required for indicating one code sequence among theplurality of code sequences are associated one to one with a pluralityof combinations of the code sequence, the cyclic shift, and theorthogonal sequence and the bits other than the bits required forindicating the code sequence are known bits.

In addition, in the communication device according to the presentdisclosure, components of the selected code sequence are multiplied bythe uplink signals each in one of the plurality of subframes,respectively.

Furthermore, according to the present disclosure, a communication deviceincludes a receiving unit that receives information indicating one of aplurality of code sequences orthogonal to one another by using a fieldfor indicating a cyclic shift and an orthogonal sequence used for ademodulation reference signal and a spreading unit that multiplies anuplink signal including the demodulation reference signal subjected torepetition across a plurality of subframes by the code sequenceindicated by the information.

In addition, in the communication device according to the presentdisclosure, the spreading unit multiplies the uplink signals each in oneof the plurality of subframes by components of the selected codesequence, respectively.

Furthermore, according to the present disclosure, a communication methodincludes selecting, from among a plurality of code sequences orthogonalto one another, one code sequence by which an uplink signal including ademodulation reference signal subjected to repetition across a pluralityof subframes is multiplied and transmitting, to a terminal for whichtransmission of the uplink signal subjected to the repetition isconfigured, information indicating the selected code sequence by using afield for indicating a cyclic shift and an orthogonal sequence used forthe demodulation reference signal.

Still furthermore, according to the present disclosure, a communicationmethod includes receiving information indicating one of a plurality ofcode sequences orthogonal to one another by using a field for indicatinga cyclic shift and an orthogonal sequence used for a demodulationreference signal and multiplying an uplink signal including thedemodulation reference signal subjected to repetition across a pluralityof subframes by the code sequence indicated by the information.

An aspect of the present disclosure is useful for a mobile communicationsystem.

What is claimed is:
 1. An integrated circuit to control a process, theprocess comprising: receiving downlink control information (DCI)transmitted from a base station to a communication device; generating ademodulation reference signal (DMRS) for a physical uplink sharedchannel (PUSCH) using a combination of a cyclic shift and an orthogonalsequence; and transmitting, from the communication device to the basestation, the PUSCH and the generated DMRS, wherein: whether thecombination used for generating the DMRS is dynamically changed or notdepends on whether the communication device is configured in a coverageenhancement mode; when the communication device is configured in thecoverage enhancement mode, in which the PUSCH is allowed to betransmitted with repetitions spanning a plurality of subframes, thecombination used for generating the DMRS is fixed and not dynamicallychanged by the DCI; and when the communication device is not configuredin the coverage enhancement mode, the combination used for generatingthe DMRS is dynamically changed by the DCI.
 2. The integrated circuitaccording to claim 1, comprising: circuitry which, in operation,controls the process; at least one input coupled to the circuitry,wherein the at least one input, in operation, inputs data; and at leastone output coupled to the circuitry, wherein the at least one output, inoperation, outputs data.
 3. The integrated circuit according to claim 1,wherein when the communication device is configured in the coverageenhancement mode, the combination used for generating the DMRS is fixedby the DCI.
 4. The integrated circuit according to claim 1, wherein whenthe communication device is configured in the coverage enhancement mode,the combination used for generating the DMRS is determined in advancebetween the communication device and the base station.
 5. The integratedcircuit according to claim 1, wherein when the communication device isconfigured in the coverage enhancement mode, the transmitting includestransmitting the PUSCH and the DMRS in a narrow band.
 6. The integratedcircuit according to claim 1, wherein the transmitting includestransmitting the PUSCH and the DMRS using a frequency hopping in anarrow band.
 7. The integrated circuit according to claim 1, whereinwhen the communication device is configured in the coverage enhancementmode, the process comprises multiplying the PUSCH transmitted withrepetitions spanning the plurality of subframes by one code sequence outof a plurality of code sequences.
 8. The integrated circuit according toclaim 7, wherein said one code sequence is determined using a field forindicating the combination used for the DMRS in the DCI.
 9. Theintegrated circuit according to claim 8, wherein the plurality of codesequences are respectively associated with a plurality of valuesindicated by bits constituting the field.
 10. The integrated circuitaccording to claim 9, wherein the plurality of values indicated by bitsconstituting the field are respectively associated with a plurality ofcombinations of the code sequences, cyclic shifts, and orthogonalsequences.
 11. An integrated circuit comprising circuitry, which, inoperation: controls reception of downlink control information (DCI)transmitted from a base station to a communication device; generates ademodulation reference signal (DMRS) for a physical uplink sharedchannel (PUSCH) using a combination of a cyclic shift and an orthogonalsequence; and controls transmission, from the communication device tothe base station, of the PUSCH and the generated DMRS, wherein: whetherthe combination used for generating the DMRS is dynamically changed ornot depends on whether the communication device is configured in acoverage enhancement mode; when the communication device is configuredin the coverage enhancement mode, in which the PUSCH is allowed to betransmitted with repetitions spanning a plurality of subframes, thecombination used for generating the DMRS is fixed and not dynamicallychanged by the DCI; and when the communication device is not configuredin the coverage enhancement mode, the combination used for generatingthe DMRS is dynamically changed by the DCI.
 12. The integrated circuitaccording to claim 11, comprising: at least one input coupled to thecircuitry, wherein the at least one input, in operation, inputs data;and at least one output coupled to the circuitry, wherein the at leastone output, in operation, outputs data.
 13. The integrated circuitaccording to claim 11, wherein when the communication device isconfigured in the coverage enhancement mode, the combination used forgenerating the DMRS is fixed by the DCI.
 14. The integrated circuitaccording to claim 11, wherein when the communication device isconfigured in the coverage enhancement mode, the combination used forgenerating the DMRS is determined in advance between the communicationdevice and the base station.
 15. The integrated circuit according toclaim 11, wherein when the communication device is configured in thecoverage enhancement mode, the transmission includes transmission of thePUSCH and the DMRS in a narrow band.
 16. The integrated circuitaccording to claim 11, wherein the transmission includes transmission ofthe PUSCH and the DMRS using a frequency hopping in a narrow band. 17.The integrated circuit according to claim 11, wherein when thecommunication device is configured in the coverage enhancement mode, thecircuitry, in operation, multiplies the PUSCH transmitted withrepetitions spanning the plurality of subframes by one code sequence outof a plurality of code sequences.
 18. The integrated circuit accordingto claim 17, wherein said one code sequence is determined using a fieldfor indicating the combination used for the DMRS in the DCI.
 19. Theintegrated circuit according to claim 18, wherein the plurality of codesequences are respectively associated with a plurality of valuesindicated by bits constituting the field.
 20. The integrated circuitaccording to claim 19, wherein the plurality of values indicated by bitsconstituting the field are respectively associated with a plurality ofcombinations of the code sequences, cyclic shifts, and orthogonalsequences.